1. Field of the Invention
The present invention concerns an ignition plug for use in an internal combustion engine and, particularly, it relates to an ignition plug to be attached upon use to the upper chamber of a cylinder in a gasoline engine, etc.
2. Description of the Prior Art
It has been known that unburnt gases remaining in the upper cylinder chamber of an internal combustion engine after the explosion stroke impair the fuel economy in the engine operation, as well as form toxic CO, NOx, hydrocarbons, etc. at high temperature in the cylinder chamber, which are exhausted externally to cause public pollutions.
In view of the above, various means have been developed and put to practical use for additionally supplying fresh atmospheric air to the inside of the cylinder chamber for the complete combustion of remaining unburnt gases. However, most of such technical means in the prior art inevitably require modification to the structure of the engine cylinder itself and yet the performance is not always quite satisfactory.
The present inventor has found that the engine torque obtained for the piston in the cylinder chamber during the explosion stroke is not caused by a uniformly expanding torque but by an impactive torque exerted irregularly on the cylinder wall, as well as that localized negative pressure (as compared with the atmospheric pressure) sometime occurs in the upper portion of the cylinder chamber at the end of the explosion stroke. Such uneven negative pressure or partial vacuum in the cylinder hinders uniform and smooth propagation of combustion flames to prevent the complete combustion of the gas mixture in the cylinder and this increased the issue of unburnt gases, which are wastefully exhausted and cause public pollutions. In addition, the negative pressure caused in the cylinder decreases the transmission efficiency of the torque to the cylinder upon explosion and, further, generates unpleasant vibrations during operation of the engine.
The present invention has already proposed a technique of additionally intaking fresh atmospheric air through the hole formed through an ignition plug by utilizing the negative pressure generated in the cylinder upon explosion stroke thereby forming a combustible gas mixture of additional air and unburnt gases and burning them again (Japanese Patent Publication No. Sho 59-23635, etc.).
In the ignition plug of our proposed structure, fresh atmospheric air is introduced by way of the air introduction channel in the ignition plug and supplied into the cylinder chamber upon sudden decrease of the pressure in the chamber at the final stage of the explosion stroke, to attain complete combustion for the unburnt gases. Further, introduction of the fresh air at low temperature can suppress NOx, CO, hydrocarbons, etc., which would otherwise result at high temperature in the cylinder, thus public pollution caused by exhaust gases can remarkably be reduced.
Further, since the unburnt gases are burnt again by the introduction of the fresh secondary air, engine torque can be increased to remarkably reduce the fuel cost. Further, since the negative pressure in the cylinder is eliminated, undesirable mechanical vibrations experienced so far in the conventional engine can be removed.
Since, the atmospheric air can be introduced into the cylinder by merely replacing existent ignition plugs with that of the present invention, it can be applied easily to any kind of engine with no difficulty.
However, ignition plugs of this type still have room for structural improvements.
Since a high voltage of about 10,000 volts or higher is applied for electric spark discharge to the ignition plug, insulators or shieldings are generally provided to the electric supply portion of the ignition plug such that neither external short-circuit nor aerial discharge results.
In the proposed plug, however, complete coverage for the plug is difficult since the central electrode used for introducing the air is inevitably exposed to the outside through the air intake port perforated in the cylindrical wall of the ignition plug. Then, high voltage applied to the central electrode may cause short-circuit failure between the electrode and other metal parts, etc. or may cause radio frequency wave troubles to electronic control devices disposed in an automobile.
There is also an additional problem that the flow rate of external air taken in through the air intake port has to be controlled depending on the capacity of engine cylinders, kind of fuels used, etc. for the complete combustion of the unburnt gases. Accordingly, since it is required to adjust the opening area of the air intake port upon mounting the ignition plug to each of the engine cylinders, it is difficult to mass-produce general-purpose plugs.